It is a technically difficult problem to achieve optical focusing in a noncontacting manner upon objects varying in size, shape, and physical properties. However, because of the fact that there are a great many uses of the noncontact focusing technique, it is a subject of study by many researchers today.
As a focusing technique generally practiced heretofore, there is an image processing technique making use of a computer. Such an image processing technique, however, has difficulties in that it requires a large-scale apparatus and is slow in performing focusing operations because of the image scanning to be executed therein. Therefore, such a technique is not considered to be practical.
The present inventor, as a result of a long period of time of earnest study in order to provide an apparatus which can overcome the aforementioned difficulties, previously proposed a noncontact automatic focusing apparatus (Japanese Patent Application No. 60-214773).
With recent progress in technology, however, there have come into existence various objects which are to be focused, such as, for example, one including a transparent substance which is difficult to optically detect, one comprising such a transparent substance and having an opaque substance or portion disposed in within its vicinity or interiorly thereof, and one which is very small in size and shape.